"Today's loser is you," he told a news conference on Monday, referring to Maduro, adding: "We won't recognise a result until every vote has been counted".

The National Electoral Council said late on Sunday that Maduro won 50.66 percent of the vote compared to 49.07 percent for Capriles - a difference of less than 300,000 ballots - allowing him to carry forward the policies of the late Hugo Chavez.

Venezuela uses electronic voting machines that print a paper ballot as a backup for any recounts.

"There should be no doubts about the election results. The institutions are functioning. If 7,500,000 Venezuelans said that Nicolas Maduro should be the president of the republic until 2019, this must be respected; the democracy and the power of the majority," Maduro said, addressing a crowd from the Miraflores presidential palace.

But, he said he would welcome an audit.

"We are calling for respect of the results. If they want do an audit they are welcome to do it. They can do whatever audit they want to do. We trust in the Venezuelan electoral system. We welcome an audit," said Maduro.

After a brief and bitter campaign, Venezuelans had waited anxiously for results into Sunday night with counting reportedly too close to call and both sides expressing confidence of victory .

"We'll see how that plays out because I'm sure the opposition is going to try and step in and say perhaps that they want a full audit before that happens. There is a long way for this to go still, the coming days are going to be key."

Recount demands

Capriles said there were attempts to let people vote after polling stations had already closed.

Turnout was 78 per cent, down from just over 80 per cent in the October election that Chavez won by a near 11-point margin.

"This result does not reflect the reality of what Venezuelans want and aspire to," he said in Caracas. "Mr Maduro, if you were illegitimate before, now you are more so.

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"I tell you firmly, this struggle is not over. It will end when Venezuela is a prosperous country when people can live better,"Capriles said.

It was unclear when a recount might start, and how long it would last.

"We demand a detailed recount in front of the world and the country," Capriles said.

Earlier, Capriles accused the government of pressuring civil servants to vote for Maduro.

Maduro inherited Chavez's formidable electoral machinery, which helped the late leader win successive elections in 14 years, with government employees often seen handing campaign pamphlets and attending rallies in groups.

Both candidates had pledged during the campaign to recognise the vote results.

Championing democracy

Capriles had hoped discontent over the nation's soaring murder rate, chronic food shortages, high inflation and regular power outages would lead him to victory.

We demand a detailed recount in front of the world and the country

Henrique Capriles, Venezuelan opposition leader

He cast his ballot in an upper-class neighbourhood, kissing a statue of the Virgin Mary after voting and urging Venezuelans to report any election abuses.

"What we want is for this country to have a true democracy, a democracy for all, a country where we can all exercise our rights without the possibility of any reprisal," he said.

Maduro was widely expected to win the right to complete the new six-year term Chavez won in October, promising to continue oil-funded policies that cut poverty from 50 to 29 percent with popular health, education and food programmes.

Chavez named Maduro, a former bus driver and union activist who rose to foreign minister and vice president, as his political heir in December before undergoing a final round of cancer surgery.